High resolution Output for Blender 2.8
I think you mean dpi – dots per inch – markets default high resolution print setting.
If you're not printing, only pixel resolution matters, and it's basically the same scenario with a different resolution:

a 3000x3000px image at 72 dpi is 105x105cm.
a 3000x3000px image at 300 dpi is 25x25cm.

A high dpi image not necessarily will be crystal clear when you zoom in. Only the size in pixels count when you're looking at the screen.